The present invention relates generally to the manufacture of a shielded, non-metallic container and, more specifically, to such a container which provides uniform and continuous shielding from electromagnetic interference and radio frequency interference.
With the increased reliance on and use of electronic instrumentation on aircraft, there has become a need to provide containers for such instrumentation which are highly sensitive to the interference generated by the myriad of electronic equipment which is present in an aircraft cockpit. Certain electronic instrumentation, particularly guidance and control instruments, are very sensitive to the electromagnetic interference (EMI) and the radio frequency interference (RFI) produced by conventional electronics and, thus, to be effective must be shielded. To this effect, EMI and RFI sensitive instruments are stored in shielded containers to block out any such interference and permit them to operate effectively.
Such containers for electronic instrumentation preferably are fabricated from materials having a high strength per weight ratio and a high impact strength. Additionally, the entire case must be uniformly electrically conductive in order to shield its contents over the entire electronic frequency spectrum. Further, the container should be resistant to temperatures in excess of about 450.degree. F. yet be capable of permitting the transfer of heat from the container.
Heretofore, different types of shielded containers have commonly been employed. One such container is a completely metallic container which is not only expensive, but is generally quite heavy and does not permit the transfer of heat from the container. Another type is an otherwise unshielded thermoplastic case having on the inner surface a silver coating which is sprayed using a spray gun. The inherent disadvantages of such a container is that not only is it quite costly due to the price of silver but uniform electrical conductivity is never achieved due to an inability to achieve a uniform distribution of the silver particles over the entire surface of the container.
Another approach to producing such a container utilizes a wire mesh which is molded into an otherwise unshielded non-metallic container. Such containers also present difficulties in effectively shielding the inner chamber due to a tendency of the wire mesh to break when molded around corners, thus breaking the electrical conductivity.
Other attempts have included the use of non-metallic containers using a powdered carbon as a conductive material but, attempts with such conductive materials also have proven unsuccessful due to an inability to obtain uniform conductivity.
Against the foregoing background, it is a primary objective of the present invention to provide a non-metallic container which is effective in uniformly shielding its contents from electromagnetic and radio frequency interference.
It is another objective of the present invention to provide such a non-metallic container which is lightweight, has a high impact strength, a high modulus of elasticity, is resistant to temperatures of at least about 450.degree. F. and is capable of permitting the transfer of heat from its chamber.
It is still another objective of the present invention to provide such a container which has a substantially uniform electrical conductivity over its entire surface.
It is yet still another objective of the present invention to provide a method for manufacturing the container of the present invention.